Ambient mass spectrometry is a recent advancement in the field of analytical chemistry and has allowed for the analysis of samples with little-to-no sample preparation. Based on this concept, a variety of ambient ionization methods have been introduced, including desorption electrospray ionization (DESI), direct analysis in real time (DART), desorption atmospheric pressure chemical ionization (DAPCI), electrospray-assisted laser desertion/ionization (ELDI), matrix-assisted laser desorption electrospray ionization (MALDESI), extractive electrospray ionization (EESI), atmospheric solids analysis probe (ASAP), jet desorption ionization (JeDI), desorption sonic spray ionization (DeSSI), desorption atmospheric pressure photoionization (DAPPI), plasma-assisted desorption ionization (PADI), and dielectric barrier discharge ionization (DBDI).
DESI is a representative method for ambient mass spectrometry. It has been shown to be useful in providing a rapid and efficient means of desorbing and ionizing a variety of target compounds of interest under ambient conditions. For example, analytes such as pharmaceuticals, metabolites, drugs of abuse, explosives, chemical warfare agents, and biological tissues have all been studied with these ambient ionization methods.
In U.S. application Ser. No. 12/205,236, DESI has been shown to analyze liquid samples without the use of filters. Still, it would be useful to use the liquid DESI apparatus in combination with electrochemical cells to allow mechanistic study of reduction-oxidation (redox) and electrolysis reactions, particularly for bioanalytical applications. In conventional applications, the coupling of EC with MS has been accomplished with ionization methods such as thermospray (TS), fast atom bombardment (FAB), and electrospray ionization (ESI). In particular, the latter method is useful in ionizing non-volatile products or intermediates of electrochemical reactions. However, in coupling EC with ESI, the EC system needs to be electrically floated, or decoupled from the ionization source to separate the high voltage operation of the ionization source from the low voltage operation of the EC cell. This decoupling increases the complexity of the apparatus and the methods of analysis. Accordingly, it would be beneficial to develop an apparatus and ionization method that simplifies the coupling of EC with MS by removing the need for electrical floating or decoupling. It would be also beneficial to remove the dead connection volume between the EC cell and the ionization source, which would shorten the coupling system response time and enable the detection of short-life transient species that are formed during electrolysis. It would be further beneficial to develop a system that has a high salt tolerance to allow for more choices in selecting electrolytes. Finally, a system is needed that can perform analysis of a small volume of sample analytes, which would allow for high throughput analysis.